Sun Photometry and Spectral Radiometry at Wavelengths Less Than 360 nm

Abstract

We report on experimental and analytical techniques for extending the useful range of sunphotometry and spectral radiometry to ultraviolet wavelengths < 360 nm. These entail modifications of the Bouguer-Langley method which allows for the spectral structure in the ozone absorption band, the detailed nature of the extraterrestrial solar flux, and round-earth corrections. Our techniques take advantage of photographic measurements of the solar aureole to provide estimates of the scattered light contributions when the instrumental solid angle exceeds that subtended by the sun. These results are also used in conjunction with absolute irradiance measurements at the ground level made with a single monochromator equipped with solar blind photomultiplier and a long-wavelength NiSO4 rejection filter. The comparison of the observations with calculations based upon the detailed extraterrestrial spectrum of Arvesen is used to determine the ozone thickness and the aerosol optical depth. We discuss the limitations of our results and work which remains to be accomplished.